The word smog comes from the words smoke and fog combined. Smog itself is formed from a mixture of these two elements and any other airborne pollutants. It first started to form in England during the first years of the industrial age. Fog, which forms from evaporated water, would grab smoke from coal factories and would trap it on the ground. This is what started to cause smog.
Today, smog is seen mostly in big cities as the yellow cloud covers the horizon. It is also easily seen during the summer when the days are hot and when the wind is weak, but it is present throughout the year.
The smog cloud is called bad ozone, because it is toxic. It is completely different from the naturally formed ozone layer located in the stratosphere, which protects us against ultraviolet rays. The ground ozone, or bad ozone as otherwise known, is the result of contact between nitrogen oxides and volatile organic compounds with sunlight. What are these elements? They are pollutants created by vehicles, industries, electricity production and other combustion processes, including burning wood.
The smog stays on the ground and is a direct consequence of human activity. It is harmful to our lungs, and especially to children, the elderly and asthmatics. Many city administrations and governments have to level the quality of the air to warn people of its danger. It is not a coincidence that more and more people suffer from respiratory problems in big cities.